Extraction of light filth from tea: collaborative study

The present AOAC method for determining insect and rodent filth in tea is time-consuming because it produced filter papers which are heavy in plant residue and therefore required long paper-reading times. A new method for the analysis of light filth in tea was developed to remedy existing problems and to improve recoveries. The method consists of the following steps: sample preparation, wet sieving, dilution with 40% isopropanol, flotation with mineral oil-heptane, and trapping off in a Wildman trap flask. In an interlaboratory collaborative study, analysts reported combined insect fragment recoveries of 99.2% for the proposed method and 93.0% for the AOAC method; the same analysts recorded combined rodent hair recoveries of 92.2% for the proposed method and 47.6% for the official method. Average times for reading individual subsamples were 9 min for the proposed method and 27 min for AOAC method. the proposed method has been adopted official first action.